Hayflick limit

The quest to live a long healthy life is a journey of universal appeal. Like the Mobius Strip at left, which has no end, there are those who pursue eternal life. As Woody Allen said, “I don’t want to achieve immortality through my work; I want to achieve immortality through not dying.”

The average lifespan in the United States has increased substantially in the last 100 years, from 47 to about 80. A major factor was the development of antibiotics in the mid-twentieth century. Recent advances in treatment of cardiovascular disease, stroke, and cancer have produced further life extensions.

Maximum lifespan is the theoretic maximum age humans can achieve. This is determined by the Hayflick limit, which defines the number of times cells can divide. To date, this lifespan generally last about 120 years. While everyone has his or her own maximum lifespan, it rarely runs to 120 years of age. The genetic factors that regulate this and are determined by one’s DNA, are mostly immutable at the current time. But the question remains: If our individual maximum lifespan is written into our DNA, how do we achieve that?

To understand how to live longer, we must first understand how and why we die short of our theoretic maximum. More importantly, what are the factors that one can alter?

Under age 45, believe it or not, the most common cause of death is accidents. In my case, at age 26, I was within seconds of dying when I encountered a problem with an airplane I was student piloting, which nearly crashed during a maneuver. Fortunately, I only managed to scare some cows (and myself). Whereas I was able to figure out the problem and avoid an untimely demise, many incidents are often difficult to avoid.

Alcohol is frequently a contributing factor in quite a large number of fatal accidents. Likewise, an alterable factor in trauma-induced death is the wearing of helmets while biking, motorcycling, and snow skiing. Actress Natasha Richardson’s tragic death to what was deemed initially to be an insignificant head trauma is only the most recent notable example. I was once asked to help evaluate the death of a female passenger who fell off the back of a motorcycle that was coming to a stop. Despite riding at a very slow speed, when she fell backwards striking her head on the pavement without a helmet, she died immediately.

It is also interesting note that since 1994, deaths from traffic accidents have steadily decreased due to mandatory seatbelts, airbags, and improved automotive design. Yet, taking its place is a different type of accident which, for the first time ever, outnumbers traffic deaths: drug-related deaths. And a leading proportion has been misuse of prescription drugs, a sadly preventable form of death.

Under age 65, the largest number of human deaths relates to cancer. Such tremendous strides have been made in cancer therapy that many cancers can now be regarded as not a death sentence but as a chronic illness if not cured entirely. The reduction in cigarette smoking has been a great help not only to cancer but even more so to preventing vascular disease. Cessation of cigarette smoking may decrease risk of vascular disease by as much as 70% in some.

Vascular disease is the largest cause of death in the over-65 age group. In fact, heart attacks and strokes account for over one-third of the annual death toll for all ages combined. This we have the biggest opportunities for prevention.

Hypertension is a significant factor in vascular disease and kidney failure. Ideal blood pressure is around 100/60. Physicians have more aggressively treated hypertension every year. Recently, treatment is recommended for pressures chronically over 130/80.

Hyperlipidemia, abnormally elevated levels of lipids or lipoproteins in the blood, is treatable in most cases and is another independent risk factor in vascular disease. The use of statins has been a leading factor toward improved health and also appears to help reduce the risk of Alzheimer’s disease.

A more subtle contribution to risk reduction has been the use of anti-platelet drugs, particularly aspirin. An effective preventive therapy for stroke and heart attack, aspirin also helps in the prevention of certain types of colon cancer and possibly breast cancer.

Prevention or treatment of obesity is also important. There are an estimated 300,000 preventable deaths annually from diabetes, for which obesity is a huge risk factor. Obesity is also an independent risk factor in many other diseases like heart disease and hypertension. Curiously, underfeeding (but not undernourishment) is well known to increase lifespan in rats. This type of underfeeding, which is really a diet aimed to achieving the lower limit of ideal weight, can positively impact health and longevity in humans as well.

Overall, although you cannot change who your parents are and the DNA they gave you, you can manipulate the environment to which the DNA is exposed and get the most out of it in terms of improved health and longevity.